If preload is your only obligation for the day, sign up for driver helper. It will supplement the days you are sent home early, or fatten that check with OT. If you're aiming beyond peak, it can't hurt your cause.
Take care of your feet. Buy Dr. Scholl's work inserts. I've never worn any type of insole prior to UPS. Now I swear by them. They really do reduce fatigue. Keep those boots laced up. I don't know how people walk around with their laces half done and tongues hanging out. Keep those ankles supported. A tight lace reduces friction and other discomfort.
Good luck.